As technical ideas capable of combining pressure sensors with other dynamic amount (i.e., physical quantity) detecting sensors in module forms, one technical idea is disclosed in JP-A-2002-286571, and another technical idea is described in Japanese magazine “DEMPA-SHINBUN HIGH TECHNOLOGY” issued by DEMPA-SHINBUN newspaper publisher on May 13, 2004.
The technical idea disclosed in JP-A-2002-286571 is related to the pressure speed sensor equipped with the pressure detecting function for detecting the air pressure of the tire and the speed detecting function for detecting the rotation speed of the tire. The pressure speed sensor is equipped with the diaphragm which receives pressure, the movable electrode and the fixed electrode which detect pressure, and the movable electrode and the fixed electrode which detect speeds. These pressure detecting movable and fixed electrodes, and the speed detecting movable and fixed electrodes are provided within the reference pressure chamber which has been hermetically closed by the housing. Both pressure and speeds are detected based upon changes in electrostatic capacitances between the movable electrodes and the fixed electrodes. Then, since the respective movable and fixed electrodes of this pressure/speed sensor are provided within the reference pressure chamber, it is possible to avoid that these movable and fixed electrodes are corroded by adhering dust and by applying acids to these electrodes.
The Japanese magazine “DEMPA-SHINBUN HIGH TECHNOLOGY” describes the tire air pressure sensor in which the pressure detecting sensor equipped with the pressure detecting function and the acceleration sensor equipped with the acceleration detecting function have been integrated in the same die. In the tire air pressure sensor, the pressure sensor (piezoelectric resistor) is equipped on the plane of the pressure film on the side of the reference pressure chamber so as to detect deformations of this pressure film, and thus, the tire air pressure is sensed based upon the detected deformations of the pressure film which separates the hermetically-closed reference pressure chamber from the air inside the tire. Also, the acceleration sensor has been provided within another hermetically-closed space which is different from the reference pressure chamber. As previously explained, since the pressure sensor and the acceleration sensor are provided within the hermetically-closed space, both the pressure and acceleration sensors can be protected from various sorts of chemical substances (remaining substances, soap, water, and the like in tire hardening process) which are present within tires.
Also, JP-A-6-347475 discloses such a structure that the acceleration sensor having the movable portion and the fixed portion, and the signal processing circuit for processing the output signal of the acceleration sensor have been stored in the package.
The technical idea disclosed in JP-A-2002-286571 has the following problems: That is, not only the structure of the sensor is made complex, but also the large number of structural members are required. Furthermore, since there are many joined portions, the air tight characteristic may be deteriorated. In addition, since these sensors must be separately manufactured, characteristic aspects of these sensors may be readily fluctuated. As a result, the technical idea disclosed in JP-A-2002-286571 has another problem that a large number of sensors having high precision can be hardly manufactured. On the other hand, the apparatus described in the Japanese magazine “DEMPA-SHINBUN HIGH TECHNOLOGY” has the following problem. That is, since the pressure sensor and the acceleration sensor are arrayed side by side to be integrated within the same die, the area occupied by these sensors becomes bulky. Furthermore, as explained in JP-A-6-347475, in the case where the sensor portion and the signal processing circuit are arranged on the same plane, there is another problem that the sensor area defined by combining the sensor unit with the signal processing circuit becomes bulky.
Thus, it is required for a physical quantity sensor to correctly sense physical quantity (i.e., dynamic amounts), and to have a structure by which an area occupied by a sensor is not made bulky.